I've been on other sites/games that have given me that error, and I knew I didn't have the info wrong. If it kept giving me the error after try a few times, I usually changed my password. I don't understand why, but that always seemed to work. Give that a try if you haven't, and if it doesn't work, just come back here and let us know.
Im currently having this issue of getting the invalid user/password problem i have changed my password twice and im still running into this issue. I have also closed the client and restarted it and still no fix. I need help. Please and thank you